Method of growing single crystals



United States Patent 3,149,910 METHOD OF GRQWDIG SllNGLE CRYSTALS Arthur Tauher, Elberon, and Robert O. Savage, In, Long Branch, N41,, assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed .lune 4, 1962, Ser. No. 200,000

1 Claim. (CI. 23-50) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to a method of growing single crystals of the formula haZn Fe O An object of this invention is to grow single crystals of the formula BaZn Fc O that are mechanically sound, have well developed crystalline faces and are relatively free of macroscopic pits and foreign inclusions. Another object is to grow single crystals of the formula BaZn Fe O for use in microwave and millimeter device applications as in isolators, rotators, filters, power limiters, and harmonic generators. A further object is to grow single crystals of the formula BaZn Pe O that can be recovered by a simple chemical treatment. A still further object is to grow such single crystals at a melting temperature sufficiently low to eliminate the problem of the reduction of Fe+ thus improving the electronic properties of the product. A further object is to grow the single crystals at a temperature that greatly reduces the loss of volatile components. Another object is to grow the single crystals in such a manner that contamination from the vessels carrying the reactants, as for example crucibles, is negligible. A still further object is to grow single crystals of the formula BaZn Fe O at least 0.1 inch in length on an edge.

The single crystal prepared by this invention is a magnetic oxide of barium, iron, and zinc having properties which makes it potentially useful as a magnetic component for applications at microwave frequencies. Single crystals are sought because: (1) The resonance line width of polycrystalline materials is so large as to limit the sensitivity and efliciency of the device in which it is incorporated; single crystals intrinsically have narrower line widths; (2) several useful properties are observed only in single crystals; (3) single crystals are important as standards by which to evaluate the performance of polycrystalline materials of the same composition.

In US. patent application Serial No. 104,483, filed April 20, 1961, there is disclosed a method of growing single crystals of formula BaZn Fe o involving dissolving a mixture of the oxides (BaO, ZnO, and Fe O in sodium carbonate at a temperature of about 13 00 C., crystallizing the compounds by reducing the temperature 15 C. per hour to between 1000 C. and 1050 C., and recovering the crystals by treating the solidified melt with hot, dilute nitric acid solution. The single crystals obtained though reducing the ferrimagnetic line width have a number of disadvantages. One disadvantage is that they do not reduce the ferrimagnetic line width sufficiently for certain applications. Secondly, the single crystals have a number of mechanical imperfections as for example pits, incompletely developed crystalline faces, etc.

We have now found a method of growing single crystals of formula BaZn Fe O that overcomes the aforementioned disadvantages. The method involves the use Bddhfilh Patented Sept. 22, 1954 ICC of bismuth oxide (Bi O as a fluxing agent. According to the method, the proper proportions of Fe O BaCO E110, and Bi O are first weighed out and then ground and mixed together dry or wet with a dispersing agent (water or ethyl acetate, etc.). The mix is then packed into a platinum crucible and heated to between 1250 C. and 1300 C. in an electric resistance furnace. The mix is then cooled at 2.5' C. per hour or slower to 1050 C.; then cooled more rapidly in a furnace to room temperature. The crystals are then removed from the crucible and freed from the flux by leaching with 10 to 20% by volume dilute nitric acid for about 8 to 25 hours. Single crystals of the formula BaZn Fe O are obtained which are substantially free of mechanical imperfections. The single crystals measure at least 0.1 inch on an edge. Compared to single crystals of the same formula grown by the Serial No. 104,483 method, the single crystals grown by the method of this invention exhibit less mechanical or growth defects and show more numerous and better formed crystalline faces. Moreover, the resonance line width of the single crystals grown by the method of this invention is about oersteds less than the resonance line width of the single crystals grown by the Serial No. 104,483 method. That is, single crystals of formula BaZn le -C grown by the Serial No. 104,483 method have a resonance line width of about 350 oersteds, whereas single crystals of formula BaZn Fe O grown by the method of this invention have a resonance line width of 250 oersteds.

In the method, the initial mixture may contain from 52.1 to 68.5 percent by weight of the mix of Bi O 6.8 to 10.3 percent by weight of the mix of BaO, 3.6 to 5.5 percent by weight of the mix of ZnO, and 21.1 to 32.1 percent by weight of the mix of Fe O The foregoing description is to be considered only as illustrative of the invention and not in limitation thereof.

What is claimed is:

The method of growing single crystals of the formula BaZn Fe O including the steps of (1) forming a ground mix from 52.1 to 68.5 percent by weight of the mix of Bi O 6.8 to 10.3 percent by weight of the mix of BaO, 3.6 to 5.5 percent by weight of the mix of ZnO, and 21.1 to 32.1 percent by weight of the mix of Fe O (2) heating the mix in a platinum crucible in an electric resistance furnace at between 1250 C. and 1300 (3.,

(3) cooling the mix at 25 C. per hour to 1050 C.,

and

(4) removing the crystals from the crucible by leaching with 10 to 20 percent by volume dilute nitric acid for about 8 to 25 hours.

References Cited in the file of this patent UNITED STATES PATENTS Remeika Feb. 26, 1963 Stuijts Aug. 27, 1963 OTHER REFERENCES 

